Well, I'm going to be honest with you, I'm kind of thick when it comes to knowing music theory (really, someone says 'key' and I immediately think of my house keys). But I'll advise you to be weary of UG, the thing there is anyone can just poast anything up. Even if the poster doesn't mean for the tabs to be wrong, they often are. I've had 3 songs there that were wrong so maybe you should try to keep searching for different sites if you have to or best of all borrow or buy a music book with 'Across the night' in it. Just to be sure.

the tab is right(from what i heard couldn't make it through the hole thing)

first let's start out with, one music is not always diatonic. meaning they(songs) don't have to follow one scale to be in a key. Next Key(tonic center) is set by harmonic progression not the scale. Scale does not equal Key. so a chord doesn't have to be the scale to be in the key.

now on to the song, the C to C maj7 bit(see in other thread you made it is necessary here) to me dose not justify a key change. the song is about dreaming so suspending the song and dwelling on C is about dreaming state thing. C Lydian would work well here if solo was going. as Frank Zappa said i can make you a sad song and happy a confused dreaming one the rules have all been set....(and goes on to what Zappa does) the little trick things in music to set moods have gotten a bad wrap do to them being see as produce. but as "the jazz theory" book says who cares use what you got there is a reason why a Augmented triad songs when Bambi comes out of the mist. so list C bit is for feel to me anyway. the next bit is a key change to G major. then i didn't get to the last bit sorry.

also I will add i agree with what jeff said

and i would start with easier songs to study because i doubt your going to get anything from this. go with simple three chord blues progression. then go on to a Beatles like thing and study there subs